Device for locking an electro-dynamically maintained balance/balance-spring

ABSTRACT

A balance locking device for an electro-dynamically maintained balance/balance-spring assembly comprises a stopping member movable between a first position in the immediate vicinity of the balance, and a second position spaced away from the balance. The balance carries at least one permanent magnet and a plate of soft magnetic material between which a soft magnetic part of the stopping member is located when the stopping member is in the first position, the magnetic forces set up locking the balance.

I United States Patent 51 3,665,699

Challandes 1 May 30, 1972 [54] DEVICE FOR LOCKING AN ELECTRO- [56] References Clted DYNAMICALLY MAINTAINED UNITED STATES PATENTS BALANCE/BALANCE-SPRING 3,262,259 7/1966 Bennett et al ..58/85.5

, 3,296,790 1/1967 Schwzulr 72 Inventor: Ch chanandes, Sonceboz Switzerland 3,526,088 9/1970 Meitinger ..58/23 [73] Assignee: Centre Electronique Horlager SA, Primary ExaminerStephen J. Tomsky Neuchatel, Switzerland Assistant Examiner-Lawrence R. Franklin Filed: Mar. 1971 Attorney-Stevens, Davis, Miller & Mosher 21 Appl. No.2 126,459 ABSTRACT A balance locking device for an electro-dynamically maintained balance/balance-spring assembly comprises a stopping [30] Foreign Application Priority Data member movable between a first positionin the immediate vicinity of the balance, and a second position spaced away May 22, 1970 Switzerland ..5657/70 from the balance. The balance carries at least one permanent magnet and a plate of soft magnetic material between which a [52] US. Cl ..58/28, 58/109 soft magnetic part of the Stopping member i located h the [51] Int. Cl ..G04c 3/04 Stopping b r i i the first position, the magnetic forces [58] Field of Search ..58/28, 85.5, 109, 63-67 set up locking the balance.

4 Claims, 2 Drawing Figures Patented May 30, 1972 v 3,665,699

2 Sheets-Sheet 1 Patented May 30, 1972 2 Sheets-Sheet 2 DEVICE FOR LOCKING AN ELECTRO-DYNAMICALLY MAINTAINED BALANCE/BALANCE-SPRING BACKGROUND OF THE INVENTION The present invention concerns a device for locking an electro-dynamically maintained balance/balance-spring. In electro-dynamically maintained timepieces, it is not possible, as in sprung-driven watches, to stop the balance by means of the winding stem by exerting, on the train connecting the barrel to the escapement, a torque opposite that of the main-spring, through a snap-on cannon pinion on the center wheel arbor, which enables momentary stopping ofthe seconds hand. To enable setting the seconds hand, there has thus been conceived a special device for locking the balance. The devices proposed up to date generally comprise a brake formed by an elastic blade which bears against a pin fixed on the balance or directly against the balance serge. These devices have certain drawbacks and certain risks of damaging the balance because of the mechanical contact between the two members. Moreover, in the first case, a minimum amplitude is necessary for operation and in the second case the locking position is not defined.

SUMMARY OF THE INVENTION It is an object of the invention to provide a balance locking device in which mechanical contact of a stopping member with the balance is avoided.

The invention therefore relates to an assembly of a balance, a balance-spring for oscillating the balance through a trajectory, and means for electro-dynamically maintaining oscillation of the balance. A balance locking device according to the invention comprises a stopping member movable between a first position in the immediate vicinity of the trajectory of the balance and a second position spaced away from the trajectory of the balance. The stopping member carries a first material and the balance carries a second material, one of the first and second materials being a permanent magnetic material and the other of the first and second materials being a soft magnetic material. The first and second materials cooperate, when the stopping member is in the first position, to set up magnetic forces to lock the balance.

DESIGNATION OF THE DRAWINGS The accompanying drawings show, schematically and by way of example, an embodiment of locking device according to the invention.

FIG. 1 is a plan view of a part of a timepiece comprising this device, and

FIG. 2 is a cross section taken along line 22 of FIG. 1.

A balance 1 forms part of an electro-magnetically maintained balance/balance-spring assembly which comprises a balance staff 2 pivoted at its two ends in bearings 3 and 4 respectively fixed to a bottom plate 5 and a balance bar 6. The balance staff 2 carries a collet 7 to which is fixed the inner end of a balance spring 8, the outer end of balance spring 8 being fixed in known manner by a stud (not shown) to the balance bar 6. A sleeve 9 is driven on the staff 2. A shoulder at the upper end of sleeve 9 supports a plate 10 carrying, on the one hand, two permanent magnets 11 and 12 fixed to an armature 13 and, on the other hand, a counterpoise 14. Plate 10 is riveted against the upper shoulder of the sleeve 9 and a second plate 15 in soft magnetic material is rivetted to the lower end of the sleeve 9. This second plate 15 has an air-gap with the magnets 11 and 12 and takes up the magnetic flux of the magnets 11 and 12 so as to form a closed magnetic circuit. The balance staff 2 also carries an impulse-pin plate 16 for driving an oscillation counting device (not shown), well known to the person skilled in the art.

The maintenance of oscillation of the balance is provided by a transistorized amplifier circuit (not shown) comprising a pick-up coil and a driving coil which cooperate with the two pennanent magnets 11 and 12. These two windings are incorporated in a flat disc-like member 17 situated between the two plates 10 and 15 of the balance, in a manner to intercept the magnetic flux of the magnets 11 and 12. i

The locking device comprises an actuating lever 18 pivotally mounted on a pillar 19 and urged towards the position shown in dotted-dashed lines in FIG. 1 by a return spring 20. An end of the lever 18 carries a small plate 21 in soft magnetic material. The other end of the lever 18 is shaped to enable the lever 18 to be moved manually from the rest position shown in dotted-dashed lines to the position shown in full lines in FIG. 1.

When the lever 18 is placed in the position shown in full lines in FIG. 2, the small plate 21 is situated inside the air-gap formed between the magnets 11 and 12 and the plate 15, and the magnetic forces set up in the air-gap formed between the small plate 21 and the magnets lock the balance. The value of this air-gap and the mass of iron in the plate 21 are determinant to provide a sufficient force able to instantaneously lock the balance. The locking position of the balance is chosen away from its rest position, that is to say away from the position in which the balance-spring 8 exerts no torque on the balance 1. Consequently, when the lever 18 is brought back to its rest position shown in dotted-dashed lines, the torque exerted on the balance 1 by the balance-spring 8 causes automatic starting up of the balance.

When the lever 18 is in the balance locking position, the magnetic force in the air-gap allows the lever 18 to be held in this locking position, against the force of the return spring 20. To bring the lever 18 back to its rest position, it suffices to manually displace the small plate 21 from the air-gap by turning the lever 18 about the pillar 19, after which the return spring 20 drives the lever 18 into its rest position shown in dotted-dashed lines. This rest position of the lever is chosen sufficiently removed from the balance so as not to perturb the period of oscillation thereof.

Operation of the described device is reliable; it requires no modification to the balance; and requires no mechanical contact between the locking device and the balance. Moreover, the device is simple to manufacture, sine it does not necessitate accurate manufacturing tolerances, and does not considerably increase the price of the timepiece.

Of course, the lever 18 can be actuated through the timesetting stem by means of a lever controlled by axial movement of the winding stem, for example.

What is claimed is:

1. In an assembly of a balance, a balance-spring for oscillating the balance through atrajectory, and means for electrodynamically maintaining oscillation of the balance, a balance locking device comprising a stopping member movable between a first position in the immediate vicinity of the trajectory of the balance and a second position spaced away from the trajectory of the balance, the stopping member carrying a first material and the balance carrying a second material, one of the first and second materials being a permanent magnetic material and the other of the first and second materials being a soft magnetic material, the first and second materials cooperating, when the stopping member is in the first position, to set up magnetic forces to lock the balance.

2. A balance locking device according to claim 1, in which the balance carries at least one permanent magnet and a plate of soft magnetic material spaced apart from said permanent magnet so as to form an air-gap therewith, the stopping member being formed of a lever comprising a part in soft magnetic material, said part being, when the stopping member is in the first position, located in the trajectory of the said air-gap.

3. A balance locking device according to claim 1, in which the balance oscillates about an equilibrium position, the first and second materials cooperating, when the locking member is in the first position, to set up magnetic forces to lock the balance when the balance is removed from its equilibrium position.

4. A balance locking device according to claim 1, comprising a spring exerting a torque on the stopping member to urge the stopping member towards the second position, the magnetic forces set up when the stopping member is in the first position being sufficient to balance said torque on the stopping member. 

1. In an assembly of a balance, a balance-spring for oscillating the balance through a trajectory, and means for electrodynamically maintaining oscillation of the balance, a balance locking device comprising a stopping member movable between a first position in the immediate vicinity of the trajectory of the balance and a second position spaced away from the trajectory of the balance, the stopping member carrying a first material and the balance carrying a second material, one of the first and second materials being a permanent magnetic material and the other of the first and second materials being A soft magnetic material, the first and second materials cooperating, when the stopping member is in the first position, to set up magnetic forces to lock the balance.
 2. A balance locking device according to claim 1, in which the balance carries at least one permanent magnet and a plate of soft magnetic material spaced apart from said permanent magnet so as to form an air-gap therewith, the stopping member being formed of a lever comprising a part in soft magnetic material, said part being, when the stopping member is in the first position, located in the trajectory of the said air-gap.
 3. A balance locking device according to claim 1, in which the balance oscillates about an equilibrium position, the first and second materials cooperating, when the locking member is in the first position, to set up magnetic forces to lock the balance when the balance is removed from its equilibrium position.
 4. A balance locking device according to claim 1, comprising a spring exerting a torque on the stopping member to urge the stopping member towards the second position, the magnetic forces set up when the stopping member is in the first position being sufficient to balance said torque on the stopping member. 